Don't add a stray period

Some output consists only of half a sentence (phrase), those should not be completed with a period, similiar to Javadoc on parameters. Moreover 'is' is not required when you use a colon.

Similar to https://github.com/codehaus-plexus/modello/commit/f969dbf051ffc7fe2d5fc6169a0291ebde4b5a54